The present invention relates to a hydraulic pump, and more particularly to a rotary-vane pump for power-assisted steering systems in motor vehicles.
In power-assisted steering systems for high speed vehicles, there is an increasing demand that with rising speed of travel the steering reaction should increase. This kind of reaction is intended to give the driver of the vehicle a reliable road feel even at high speeds. However, the increased delivery power of the pump at higher rotational speeds increase the hydraulic steering assistance, and the proportion of mechanical power to be supplied by the driver is reduced. A reliable road feel is therefore lost.
The invention aims at providing a hydraulic pump wherein with rising rotational speed of the pump, the delivery of pressure hydraulic fluid flow is reduced.
Specifically an object of the present invention is to provide a hydraulic pump which, without any external assistance, reduces the delivery of pressure hydraulic fluid flow at higher rotational speeds of the pump.